Initial interest in the use of sodium oxybate as a potential treatment for narcolepsy arose from observations made during the use of sodium oxybate (known as gamma-hydroxybutyrate in older literature) for anesthesia. Unlike traditional hypnotics, sodium oxybate induces sleep that closely resembles normal, physiologic sleep (Mamelak et al., Biol Psych 1977:12:273-288). Therefore, early investigators administered gamma-hydroxybutyrate (GHB) to patients suffering from disorders of disturbed sleep, including narcolepsy (Broughton et al. in Narcolepsy, NY, N.Y.: Spectrum Publications, Inc. 1976:659-668), where it was found to increase total nocturnal sleep time, decrease nocturnal awakenings and increase Stage 3-4 (slow wave) sleep. Three open-label and two placebo-controlled studies provided a body of evidence demonstrating that improvements in nocturnal sleep were associated with a reduction in cataplexy and improvements in excessive daytime sleepiness (Broughton et al., Can J. Neurol Sci 1979; 6:1-6, and Broughton et al., Can J. Neurol Sci 1980; 7:23-30)
Scharf et al. conducted an open-label study to evaluate the effects of GHB on the sleep patterns and symptoms of non-narcoleptic patients with fibromyalgia (Scharf et al., J Rheumatol 1998; 25: 1986-1990). Eleven patients with previously confirmed diagnosis of fibromyalgia who reported at least a 3-month history of widespread musculoskeletal pain in all body quadrants and tenderness in a least 5 specific trigger point sites participated in the study. Results showed that patients reported significant improvements in the subjective assessments of their levels of pain and fatigue over all 4 weeks of GHB treatment as compared to baseline, as well as a significant improvement in their estimates of overall wellness before and after GHB treatment.
WO 2006/053186 to Frucht describes an open label study of 5 patients with hyperkinetic movement disorders including ethanol responsive myoclonus and essential tremor. Sodium oxybate was reported to produce dose-dependent improvements in blinded ratings of ethanol responsive myoclonus and tremor and was said to be tolerated at doses that provided clinical benefit.
Xyrem® sodium oxybate oral solution, the FDA approved treatment for cataplexy and excessive daytime sleepiness associated with narcolepsy, contains 500 mg sodium oxybate/ml water, adjusted to pH=7.5 with malic acid. In man, the plasma half-life of sodium oxybate given orally is about 45 minutes and doses of 2.25 grams to 4.5 grams induce about 2 to 3 hours of sleep (See, L. Borgen et al., J. Clin. Pharmacol., 40, 1053 (2000)). For optimal clinical effectiveness in narcolepsy, sodium oxybate must be given twice during the night, and is administered as an aqueous solution. For each dose, a measured amount of the oral solution must be removed from the primary container and transferred to a separate container where it is diluted with water before administration. The second dose is prepared at bedtime and stored for administration in the middle of the night. This regimen is cumbersome and prone to errors in the preparation of the individual doses. For this reason, a more convenient unit dosage form of the drug would be clinically advantageous. Sodium oxybate is highly water-soluble, hygroscopic and strongly alkaline. Paradoxically, despite its high water solubility, it forms a gel when dissolved in water. These properties, along with the large amount of the drug that is required to achieve the clinical effect, present challenges in preparing solid unit dosage forms that are designed for immediate release of the sodium oxybate into the gastrointestinal tract of the user.
L. Liang et al. (published U.S. patent application US 2006/0210630 A1) discloses administration of gamma-hydroxybutyric acid using an immediate release component and a delayed/controlled release component. The immediate release component is disclosed to be an aqueous solution, or a “solid pellet, bead or mini tablet.” While the pellets disclosed in Example 1 comprise as much as 80-90 wt-% sodium gamma-hydroxybutyrate, they are the immediate release portion of the controlled release dosage form and are not formed into a compressed tablet. They are added to other forms of sodium oxybate to prepare controlled release dosage forms.
A continuing need exists for solid immediate release dosage forms of sodium oxybate that can deliver therapeutically effective amounts of sodium oxybate following in vivo administration and which have pharmacokinetic profiles similar to that of the oral solution.